1. Field of the Invention
The present invention relates to a process for producing homopolymers and copolymers of propylene and copolymers of propylene and other unsaturated hydrocarbon monomers. More specifically, the present invention relates to a process which comprises carrying out a polymerization in liquid propylene (hereinafter, designated "bulk polymerization" for brevity) and obtaining a homopolymer of propylene and/or a copolymer of propylene and other unsaturated hydrocarbon monomers, such as ethylene.
2. Description of the Prior Art
Bulk polymerization is well known, has been carried out on a commercial scale and is quite advantageous. The vapor pressure of the solvent, which is unsaturated hydrocarbon monomers of which the greater part is propylene, in the polymer slurry obtained by bulk polymerization is higher than that of the conventional slurry or solvent polymerization which uses liquid saturated hydrocarbons having more than 5, preferably from 5 to 7, carbon atoms as a solvent (hereinafter, designated "conventional slurry polymerization" for brevity), so the polymer produced can be easily separated from the slurry simply by reducing the pressure.
However, generally some disadvantages exist with the polymer separated from the solvent using the above described method. Firstly, the polymer contains a large amount of polymer soluble in boiling n-heptane. Secondly, the polymer contains a large amount of catalyst residues. It is essentially possible to reduce catalyst residues in the bulk polymerization, because the polymerization reaction rate is faster than that of the conventional slurry polymerization and the polymerization can be carried out at a desirable catalyst efficiency.
Therefore, the omission of the slurry treatment process which removes the polymer soluble in boiling n-heptane under the above described conditions enables a significant economic effect to be achieved.
The polymer obtained by the above described method in which the slurry treatment process is not used, however, has the following disadvantages in quality.
For example, the polymer obtained using a catalyst system of titanium trichloride and triethylaluminum contains only 75 to 85% by weight of polymer insoluble in boiling n-heptane, and in the case of using a catalyst system of titanium trichloride and a diethylaluminum halide the amount of the polymer insoluble in boiling n-heptane is 85 to 95% by weight.
The properties of the above described polymer are in particular not good with respect to stiffness and tackiness. The polymer, therefore, can be used as a moulding grade polymer but it is impossible to use the polymer as a film and fiber grade polymer since a film and fiber grade polymer must have superior quality.
For the purpose of improving the properties of the polymer, generally, the polymer slurry withdrawn from the polymerization zone or the polymer separated under reduced pressure from the unsaturated hydrocarbon monomers, of which the main portion is propylene, is treated with suitable catalyst deactivators, and then washed using a solvent which consists mainly of a saturated hydrocarbon liquid having 5 to 7 carbon atoms or a liquid unsaturated hydrocarbon monomer such as the propylene being polymerized in the reaction zone, whereby the solvent-soluble polymer and catalyst residues are extracted and removed.
The above described catalyst deactivators are agents which decompose the active catalysts and/or terminate the polymerization reaction by forming a complex compound with the catalysts suppressing the formation of high molecular weight polymer which degrades the quality and furthermore in the following washing zone, facilitate extraction of the treated catalyst residues into the solvent.
These catalyst deactivators are, generally, alcohols, ethers, ketones and chelating agents and so on. The deactivators can be used as they are or diluted with the same solvent used in the above described processing as a diluent.
To reduce the formation of the solvent-soluble polymer, the following various methods are generally adopted.
For instance, in one method a catalyst system consisting of the complex compound of titanium halide and aluminum halide is used. In another method compounds which are described hereinafter as the third component are added to the catalyst system or the polymerization system to improve the polymerization conditions such that the polymerization reaction temperature can be reduced. In the above described methods, a fairly large amount of the solvent-soluble polymer is produced and it is difficult to omit the process for removal of the above described solvent-soluble polymer.